In the late 70's when they really started cracking down on emmissions and transistorized ignition systems came along car makers really increased ignition secondary voltage. The wide cap distributors were designed to eliminate cross firing. That said, the main benefit that I can see for them is that they allow the use of the pretty blue Motorsport wires (that's why I bought and installed mine.). They come in bakelite grey, the cap has aluminum terminals and the rotor has a stainless/brass terminal. Carquest auto parts has the adaptor and the cap in their premium brand which is blue. Both the rotor and cap are advertised with brass terminals. Likewise, the adaptor/cap/rotor are also available from Borg Warner (Pep Boys) in both standard (aluminum terminals) and select (brass terminals), and Accel. When I recently replaced my cap and rotor from the Motorsport kit I asked for parts for a 1979 V8 Granada (thanks to suggestions from VMF) and everything went smooth (except that the Pep Boys parts guy gave me a wrong part and I had to go back and get the right one).